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Proposed B.C. mine plans to reduce water content in waste but still use tailings dams

Author of the article:

Gordon Hoekstra

Publishing date:

December 31, 2015 • 4 minute read

Geologist Renee Potvin and environmental scientist Rob Maciak looking over the site of KGHM International’s proposed Ajax copper and gold mine. The pit in the photograph is pre-existing from a past mining operation.Handout

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KGHM International’s proposed Ajax copper and gold project will be one of the first tests of the B.C. government’s approval of waste storage for large open pit mines after the Mount Polley mine dam failure in 2014.

The company, whose parent is Polish company KGHM Polska Miedz SA, plans to submit its project application early this month for review by the B.C. government. It will kick off an 180-day environmental assessment.

The $795-million project is controversial and has met with community resistance, in part, because of its proximity to Kamloops.

KGHM proposes to reduce water quantities in its mine-waste facility — and entirely buttress the large dams with rock — to increase safety at the planned mine.

However, it will not be using the dry-stacking technique to store mine waste as planned in its initial design. That method recommended by an engineering panel appointed by the B.C. government to investigate the Mount Polley failure.

Under the dry-stacking method, water is squeezed out of the finely ground rock that remains after the ore is processed. The waste rock is then transported to a storage area and compacted. The rock, which can contain toxic metals, is commonly called tailings.

The engineering panel’s report recommended the dry-stack method because there is no dam to fail, and if dry-stacked tailings shift, such as a result of an earthquake, they will not go as far as water-saturated tailings.

Among the largest spills in the world in the past 50 years, the catastrophic failure at the Imperial Metals’ Mount Polley mine released millions of cubic metres of tailings into the Quesnel Lake watershed, completely scouring a nine-kilometre creek.

Based on its own analysis of best-available technology, KGHM says it plans to thicken its tailings by squeezing out a lot of the water, increasing the solid content to 60 per cent from the 32 per cent typical of conventional mines tailings.

The tailings will be stored behind rock-and-earth dams that will reach a height of 120 metres. Water will still be stored on top of the thickened tailings, but there will be less water than under the method used at Mount Polley.

The use of thickened tailings will allow the mine to reduce the size of the mine waste storage facility, although with a capacity of 440 million tonnes, it will be much larger than the Mount Polley facility, which stored about 90 million cubic metres of tailings when the dam failed.

“I think what sets Ajax apart in the world of tailings embankment is the huge (rock) buttress and also that we are going to thicken our tailings,” says Clyde Gillespie, project development manager for Ajax.

Even though dry-stacking is considered well-suited to arid or semi-arid regions, Gillespie said they rejected dry stacking because it has not been proven at the large size of mine they will operate, which will process 65,000 tonnes of ore a day. The largest dry-stack operations are in the 20,000-tonne-a-day range, he noted.

“There are a lot of challenges when you make that type of three-fold increase in throughput,” said Gillespie.

He said they also were responding to concerns from the community that dry-stacking would create dust and noise.

John Schleiermacher, a spokesman for the group Stop Ajax Mine, said they are not much impressed with the plan for thickened tailings. However, the group also had concerns with dry-stacking.

Schleiermacher said the proposed mine is simply too big and too close the city of Kamloops, with a population of 86,000.

“I am sure they are going to do best to protect the community from a tailings pond breach. But you can’t guarantee it’s not going to happen,” he said.

Thickening tailings goes part way to meeting the intent of the recommendations of the Mount Polley engineering panel, but ultimately the panel was talking about removing all water from the tailings, said David Chambers, a geophysicist who heads the U.S.-based Center for Science and Public Participation, a group that provides analysis and advise on environmental issues related to mining.

The group wrote a report last year on risk and public liability of tailings storage facilities following the Mount Polley failure.

“The big question for companies to answer is how are they meeting the overall recommendations from the Mount Polley engineering panel?” said Chambers. “You have to put safety over cost — because dewatering the tailings is a safety issue,” he said.

How the B.C. government will assess the KGHM’s analysis of its proposed mine waste storage plan and the alternatives they examined remains to be seen.

It is clear, though, the province has asked mining companies to examine, and in some cases, re-examine their mine-waste storage plans in light of the recommendations from the government-commissioned engineering panel.

Earlier this year, the province ordered Pacific Booker to re-examine its waste storage plans at its proposed $517-million Morris copper-gold-molybdenum-silver project in north-central B.C. Yellowhead Mining was ordered to do the same for its $1.03-billion Harper Creek copper-gold-sliver mine in the Interior.

Harper Creek asked for a suspension of its government environmental review to have time to gather more information and then announced in October it was postponing plans because of low metal prices.

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